.toc{background-color:#eef7fa;padding:20px;border-left:4px solid #3498db;margin:25px 0;border-radius:5px}.toc h2{margin-top:0;border-left:none;padding-left:0}.example{background-color:#e8f6fc;padding:15px;border-left:4px solid #2ecc71;margin:20px 0;border-radius:5px}.rule{background-color:#fff8e1;padding:15px;border-left:4px solid #f39c12;margin:20px 0;border-radius:5px}.exercise{background-color:#eef7fa;padding:20px;border:1px solid #3498db;margin:25px 0;border-radius:5px}.answer{color:#27ae60;font-weight:700}.mistake{color:#e74c3c;text-decoration:line-through}.note{background-color:#f5eef8;padding:15px;border-left:4px solid #9b59b6;margin:20px 0;border-radius:5px}